中文摘要：

北斗导航卫星系统BDS已在新一代试验卫星星座上成功实现了星间链路（ISL）相互伪距测量.对时分体制Ka频段星间钟差测量实测数据的分析表明,虽然星间钟差测量的随机误差水平达到了10 cm（RMS）水平,但其中仍包含显著的系统性测量误差.该系统误差严重影响了星间链路测量在星间时间同步和提升轨道精度等方面的应用.分析表明,该系统误差来源于星间链路信号收发设备的时延.该时延在地面环境难以标定,且地面标定值在卫星入轨和在轨工作期间受空间环境影响可能发生变化.本文利用BDS星地L双向时频传递设备采集的星地钟差数据,以及星间链路测量数据,对星间链路收发设备的组合时延进行最优估计.估计的具体策略是对任意一个卫星对,利用这两颗卫星的星地钟差数据以及星间链路数据,解算这两颗卫星星间链路设备的组合时延.对2IGSO/2MEO新一代试验卫星星座连续14 d的数据处理结果表明,每天对每颗卫星解算一组星间链路组合时延值,该时延值的时间序列具有较好的稳定性,其在14 d内的标准偏差小于0.3 ns.将获得的组合时延值应用于星间相对钟差的测量,星间链路对地数据测定钟差与星地L双向钟差测量结果得到的钟差具有较好的一致性,证明了组合时延的自洽性.结果表明,星间链路数据对MEO卫星境外弧段钟差预报精度提升尤为明显：钟差监测弧段提升达到全弧段的40%以上;卫星入境后,M1S预报误差从3.59降低至0.86 ns,M2S从1.94降低至0.57 ns.

英文摘要：

The new-generation Beidou satellites constellation consists of 2 inclined geosynchronous orbit（IGSO） satellites and 3 medium orbit（MEO） satellites. The inter-satellite ranging payloads onboard provide the constellation with autonomous navigation capability. Each satellite navigates using the rest of the satellites in the constellation. The satellites perform two-way time division multiple access（TDMA） inter-satellite link（ISL） ranging using pseudo random codes. For some reasons, the global system of Beidou navigation satellite system（BDS） will still depend on its regional station net, which is not able to observe medium orbit satellites for the whole section. The ISL ranges also make it possible for BDS to obtain clock and orbit observables when the satellites cannot be seen by its limited regional stations. While ranging, the system errors of TDMA payloads on new-generation Beidou satellites must be considered, which are hard to calibrate on the ground and will affect the accuracy of inter-satellite time synchronization and orbit determination. In this paper, a calibration method of inter-satellite system error is proposed, and the application of ISL ranges on satellite-ground time synchronization is discussed. Firstly, the using strategy of ISL clock offset is discussed. The satellite-ground part obtained by L-band two-way satellite time frequency transfer（TWSTFT） is introduced and the satellite-satellite part obtained by inter-satellite link is modeled to obtain the clock and orbit observables. Broadcast ephemeris is used to decouple the inter-satellite clock offset and inter-satellite range, and the observation equations are provided. Secondly, the L-Band clock offset is used to calibrate the combined system error of each inter-satellite payload. By comparing inter-satellite clock offsets of a pair of satellites obtained by ISL with satellite-ground clock offsets of the same two satellites obtained by TWSTFT, a combination of signal transmitting delay and signal receiving delay is cali